A wide variety of pigment dispersants and resin dispersions has been developed to date for various use, and their applications range across extremely diverse products. Concerning pigment dispersants, for example, known products include those of the comb structure each obtainable by reacting a polyester of a carboxylic acid, which has a single terminal COOH group, with a polyamine (Patent Document 1); those each obtainable by reacting a solvent-soluble polymer and a compound having one or more functional groups as pigment-adsorbing groups with an isocyanate (Patent Document 2); and those each obtainable by subjecting styrene and an acrylic monomer to random copolymerization (Patent Document 3).
As resin dispersions, on the other hand, there are water-based resin dispersions each obtainable by neutralizing an acrylic or acrylic styrene resin of low molecular weight to dissolve it in water, adding a monomer to the resulting system and then polymerizing them (Patent Document 4); and non-aqueous resin dispersions each obtainable by adding, in the presence of a macromonomer obtained by reacting glycidyl methacrylate, another radical polymerizable monomer to a methacrylate polymer containing at an end thereof a residual carboxyl group of a chain transfer agent such as mercaptoethylcarboxylic acid and having a long-chain hydrocarbon group of eight carbon atoms or a like number of carbon atoms soluble in an aliphatic hydrocarbon solvent (Patent Document 5).    Patent Document 1: JP-A-11-197485    Patent Document 2: JP-A-04-210220    Patent Document 3: JP-A-01-164429    Patent Document 4: JP-A-04-053802    Patent Document 5: JP-A-55-035321